I use a Nikon D7000 - it's already quite capable of producing clean files up to 5000, 6400 at a pinch, and of getting perfectly sharp pictures of the cars running in night qualifying at Le Mans earlier this year (admittedly with pretty fast glass). No way I'm pointing a flash at a live race track at night, even if there was a way to make the results look even slightly natural.... So, IMHO, that milestone was crossed some time ago and has been in the high-end consumer space for at least a year now.

What this has primarily done for me is to make non-studio flash for fill and separation, depending on the situation - to control the subject to ambient ratio, in other words. I do still use it for other routine work, but only where it makes the resulting shot easier to take and get a high-quality result.